The invention relates to a single-control change gear of the desmodromic type, usable in particular in motor vehicles.
At present in the field of mechanics different devices are used which permit of varying, at the driver's will, the movement velocity ratio between the origin of the said movement and the user element, or more precisely to vary the velocity ratio, that is the ratio between the velocity of the driven organ and the drive organ.
For example, as regards motor vehicles, the abovementioned organs are constituted by: a main shaft, rotated directly by the drive shaft, on which main shaft a series of cogged wheels are arranged, coaxially and keyed on to the said main shaft, said cogged wheels being equivalent in number to the number of ratios which are present in and can be effected by the gearshift device; a driven shaft, arranged parallel to the main shaft, also equipped with a corresponding series of normally idle cogged wheels and in constant mesh with the preceding cogged wheels. Between the shaft pair and the drive shaft a friction device is interposed, with which it is possible to connect the entire change group to the said drive shaft; to perform the engagement of the various ratios between the main shaft and the driven shaft there are various solutions and the most frequently used of these comprise a key or a plurality of ball bearings: the first uses a longitudinally sliding key internal to the driven shaft, activated by means of the usual lever mechanisms constituted by a fork shift manoeuvrable by the operator, with which for each gear change one of the cogged wheels is keyed to the driven shaft. The second of the above solutions envisages a slidable spindle, as above longitudinally slidable internally to the driven shaft, moved by the user (still by means of the fork-shift) and destined to mesh, as above for every gear change, the selected cogged wheel by means of a plurality of ball-bearings arranged radially to the shaft and interpositionable between the said shaft and the cogged wheel.
All of these solutions are, however, mechanically weak, in that the driven shaft is realised either with a longitudinal groove of considerable dimensions to permit of the passing 05 of the key, or with a plurality of circular apertures distributed on the circumference for containing the ball bearings; furthermore, the driven shaft in the case in which numerous velocity ratios are used, would tend to bend, given the considerable length that would be necessary to position all of the wheels, or might require the use of intermediate supports which would lead to a further increasing of the dimensions of the gearshift group.
Thus, such solutions can exclusively be used for transmissions of lesser power and having a small number of velocity ratios, in order not to act negatively on the shaft length.
The aim of the present invention is to eliminate the above-described drawbacks, by providing a change gear with a command shaft equipped with desmodromic-type meshes, compact in its dimensions, especially in its axial dimensions, precise and fast in its meshing and thus able to permit of a high number of velocity ratios.
A further aim of the present invention is to realise a change gear with regularly distributed meshes along the circumference of the command shaft so as not negatively to influence the change gear's strength; this leads to the possibility of transmitting high couples between the motor and the transmission.